1. Field of the Invention
This invention relates to an electronic timepiece which consumes small amount of electric power.
2. Description of the Prior Art
In electronic timepieces, electric power of a battery is consumed by a quartz oscillation circuit, frequency divider, pulse motor, time display device composed of electro-optical display elements and leakage current loss of a battery. The operative life of the electronic timepiece is determined by the relation between the above mentioned consumed electric power and the current capacity of the battery.
In the case of producing the electronic timepieces in commercial scale, it is important to put stress not only on the characteristic thereof but also on the above mentioned operative life and design.
The recent techniques render it possible to improve the characteristic of the pulse motor and to rationalize the design of wheel mechanism such that the electric power required for driving the timepiece is decreased from 10 .mu.W required in several years ago to 1 .mu.W required at present. The electric power required for displaying times of the electronic timepiece with the aid of a liquid crystal, for example, is at most 0.5 .mu.W. As a result, the electric power required for displaying times can be supplied from a battery having a capacity which is 1/10 times smaller than that required in several years ago. In addition, it is possible to design a timepiece which can operate for 10 years long.
At present, constitutional elements of the electronic timepiece other than the time display device consume an electric power of 3 .mu.W of 1.5 .mu.W. 2/3 of such electric power is consumed by an oscillation circuit and 1/3 is consumed by timepiece circuit other than the oscillation circuit such as a frequency divider or the like. As a result, at present 2/3 of the drawback of preventing the battery from becoming long in operative life consists in the electric circuit. In addition, a complementary metal oxide semiconductor integrated circuit constituting the electric circuit of the electronic timepiece consumes that electric power which is proportional to the square of the electric supply source voltage.
A lithium battery can be made so small in size that it can be incorporated into an electronic wrist watch. In addition, the lithium battery can preserve its large electric power capacity for a long time. But, the lithium battery generates a high voltage of 2.6 V to 3.2 V which is not suitable as an electric supply source for the timepiece circuit and has a voltage changeability which is higher than that of a conventional silver battery. As a result, the lithium battery could not be applied to the electronic timepiece so as to utilize its excellent electric characteristics for the purpose of making the electric timepiece long in its operative life.